[scytheavatar]

I am thinking of including one for my 3 channel B22. I don't mind the popping sounds but I am a bit afraid of the damage that the DC offsets can deal to my headphones. So is it worth it to build a ε12 for my B22? Will it degrade my sound quality in any way? Thanks.

 

[FallenAngel]

The Beta22 doesn't have DC offset, you zero it out when you set it up

 

[amb]

... Neither should β22 emit any popping noise when being powered on or off.

On the other hand, a main function of the ε12 is to protect the headphones from an abnormal DC offset due to malfunction. Whether it's worth it or not depends on your comfort level with the reliability of your build.

 

[luvdunhill]

Quote:

Originally Posted by amb /img/forum/go_quote.gif ... Neither should β22 emit any popping noise when being powered on or off. On the other hand, a main function of the ε12 is to protect the headphones from an abnormal DC offset due to malfunction. Whether it's worth it or not depends on your comfort level with the reliability of your build.

... and how thermally stable things are. For example, what's the DC offset right when the amp is turned on, 1 minute later, and 3 hours later...

 

[MisterX]

The MOSFETs used in the Beta22 have a negative temperature coefficient.
The DC offset actually goes down as the amplifier warms up.

 

[amb]

Once it's been nulled with the trimpot, β22's DC offset should be quite stable, never varying more than a couple of mV this way or that. This is true whether the amp is just powered on, or after many hours (or days) of running.

The negative tempco of the MOSFETs doesn't affect DC offset, but it does reduce the quiescent current as the amp warms up, preventing thermal runaway.

 

[luvdunhill]

this wasn't the case with one that I fixed. Once the lid went on, the offset jumped up 20mV or so. Some of these builds are so packed in, that its not hard to believe that the MOSFET heat of one board is effecting the front end offset of another.

 

[amb]

Heat alone isn't going to introduce DC offset. You'd have to have a significant heat gradient between β22's Q1 and Q2 (or Q3 and Q4) to make the DC offset drift away. Since these JFETs are located right next to each other this situation should be minimal, and on the v1.02 PCB you could even get the JFETs' flat faces to partially "hug" each other to really reduce these effects.

Nevertheless, 20mV of DC offset is far from harmful, and is much less than the trigger threshold of the ε12 protection circuit.

 

[Navyblue]

If B22 doesn't really benefit from having an E12, what sort of amp would especially benefit from it? HV tube amp? Or any tube amp including hybrid?

The SOHA II board have one built in, I have heard someone mentioned that Millet SS would benefit from one.

So these are amps have a tendency to damage headphones when it is turned on or when parts fail?

 

[amb]

Many amps emit a "pop" when turned on, as well as a big DC offset shift. A similar offset shift may also occur at turn-off. The muting/delay aspect of an ε12 would be good for such amps.

Almost any single-rail amp (but having no virtual ground) with a large-ish output coupling capacitor would fall into this group (and this includes most tube amps and tube-hybrids). Even some dual-rail SS amps exhibit turn-on noise.

β22 is a notable exception. Its fully complementary topology from input to output ensures all parts of the circuit bias up and down in symmetrical fashion. Along with the σ22 power supply which exhibits a very gentle voltage ramp-up when power is applied, and the tracking design means that the rail voltages are always equal, results in virtually noiseless turn-on and turn-off.

 

[Navyblue]

Thanks again AMB.

I'm glad that I ordered one last night (yeah that was me

). I figured it would come in handy for my future tube/hybrid build. Man I became one of those who started hoarding parts for future build even when current build is far from over.

 

[Uncle Erik]

Quote:

Originally Posted by Navyblue /img/forum/go_quote.gif Man I became one of those who started hoarding parts for future build even when current build is far from over.

What do you mean "one of those?"

Hoarding is required by law after you finish your first working amp.